Yuntao Li

High-performance proton exchange membranes for direct methanol fuel cells based on a SPEEK/polybenzoxazine crosslinked structure

Sulfonated poly(etheretherketone)/polybenzoxazine (SPEEK/PBa) crosslinked blends were prepared as a proton exchange membrane (PEM) for direct methanol fuel cell (DMFCs) application. SPEEK catalyzed the ring-opening polymerization of benzoxazine (Ba) monomers and then reacted with PBa to form a crosslinked membrane with greatly improved mechanical integrity. Extraction testing, Fourier-transform infrared, and X-ray photoelectron spectroscopy results indicate that the crosslinking reaction took place at 150 °C between the SPEEK and PBa. The crosslinked SPEEK/PBa structure gives a better dimensional stability, thermal stability, and mechanical integrity than the SPEEK membrane alone. The proton conductivity of the SPEEK/PBa-15% membrane is 4.25 × 10−3 S cm−1 at 30 °C, and reaches 2.46 × 10−2 S cm−1 at 80 °C. The methanol diffusion coefficient of the SPEEK/PBa-15% is reduced by 93% when compared to a Nafion-117 membrane under the same testing conditions. The maximum selectivity at 80 °C is 4.45 × 103 S s cm−3 for SPEEK/PBa-15%, which is nearly 1.3 times higher than that of a Nafion-117 membrane. The observed excellent properties of SPEEK/PBa membranes are attributed to the uniformly crosslinked structure of SPEEK/PBa and the rigid backbone of PBa.

Thermal curing of novel carborane-containing phenylethynyl terminated imide oligomers

A novel carborane-containing phenylethynyl terminated imide compound (Carb-PEPA) as a modifier for fluorinated phenylethynyl terminated imide oligomer (AFR-PEPA) was synthesized and characterized by FT-IR and 1H-NMR. The resin systems consisting of Carb-PEPA and AFR-PEPA (AFR-PEPA-Carb) were prepared with different weight fractions of Carb-PEPA. The thermal curing kinetics and thermal stability of the imide compound and resultant resin systems were analyzed by using DSC and TGA respectively. The relevant kinetic data were determined by a Kissinger method. The results show that the glass transition temperatures (Tg) of the cured resin systems increase with the addition of Carb-PEPA. The imide system containing 20 wt% Carb-PEPA (AFR-PEPA-Carb-20) exhibits the highest Tg of 389.5 °C due to the high steric hindrance of carborane. The char yield of the resin was also increased with the introduction of the carborane structure in the system. The kinetic data indicate that AFR-PEPA/Carb-PEPA imide blends have higher activation energy E and frequency factor A than AFR-PEPA imide oligomers.

Flame retardation behavior of polybenzoxazine/α-ZrP nanocomposites

Flame retardation behaviors of polybenzoxazine (PBa) nanocomposites containing various levels of exfoliated α-zirconium phosphate (α-ZrP) nanoplatelets were prepared and confirmed by transmission electron microscopy. Thermogravimetric analysis (TGA) and cone calorimetry results indicate that exfoliated α-ZrP could drastically enhance the thermal stability of PBa and promote high char formation of PBa. Additionally, α-ZrP greatly enhances the flame retardancy of PBa. The time to ignition was increased to 91 s for PBa/α-ZrP-4.6 wt% as opposed to 73 s for pristine PBa. The peak heat release rate value of PBa was significantly reduced by nearly 50% with 8.4 wt% addition of α-ZrP. The char residue analyses using scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy suggest the participation of α-ZrP in the charring process. The volatile products formed in the thermal degradation processes of PBa and PBa/α-ZrP were analyzed by a TGA-Fourier transform infrared spectrometer and found that exfoliated α-ZrP facilitate the formation of a compact and homogeneous char layer, which contains flame retardant elements (N, P and Zr) on the surface of the materials, during burning. The improved flame retardancy of PBa/α-ZrP is mainly attributed to a combination of the greatly increased melt viscosity of PBa and matrix fast swelling due to the formation of the pyrolytic gases. Additionally, exfoliated α-ZrP is found to greatly reduce the amount of toxic gases containing C–O groups. Instead, it releases phosphorous-containing species to achieve flame retardancy in the gas phase. The implication of the present study for the preparation of fire retardant polymers is discussed.

Flame retardant and toughening mechanisms of core–shell microspheres

Epoxy (EP) composites containing polystyrene-ammonium polyphosphate core–shell microspheres (CSPPS-APP) were developed for flame retardant and toughening effects. The flame retardancy and thermal degradation behavior of the EP composites was investigated by limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter (CONE) and thermogravimetric analysis (TGA). Scanning electron microscopy with energy-dispersive spectroscopy capability (SEM-EDS) was used to characterize the morphology and elements of the residual chars. A possible flame retardant mechanism of the CSPPS-APP in EP matrix was proposed based on the CONE, TGA and SEM-EDS results. The influence of CSPPS-APP content on the glass transition temperature (Tg), storage modulus, Youngs modulus, tensile strength and fracture toughness (KIC) of the material was also investigated. The results show that the CSPPS-APP microspheres lead to significant flame retardant and char formation effects on the EP. The Youngs modulus and fracture toughness of the EP/CSPPS-APP composites increase with increasing CSPPS-APP content. The fracture toughness of the composite containing 15% CSPPS-APP increased by approximately 59% compared to that of the neat matrix. In addition, the critical strain energy release rate (GIC) of the epoxy increased from 159 to 409 J m−2 with the addition of 15% CSPPS-APP. The SEM images of the fracture surface indicate that the enhanced toughness of EP/CSPPS-APP composites can be attributed to the debonding of the core–shell microspheres and the subsequent plastic void growth of the matrix, as well as the crack deflection effect of CSPPS-APP.

Preparation and properties of semi-IPN proton exchange membranes based on SPEEK and cross-linked PSt-DVB for direct methanol fuel cells

Sulfonated poly(ether ether ketone)/poly(styrene-divinylbenzene) (SPEEK/PSt-DVB) semi-interpenetrating polymer networks (semi-IPNs) were prepared to be used as proton exchange membranes (PEMs) for direct methanol fuel cells (DMFCs) applications. The morphologies of the membranes were investigated using field emission scanning electron microscopy. The ion-exchange capacity, water uptake, proton conductivity, methanol permeability, mechanical properties, and the thermal stability were characterized for each of the various semi-IPN membranes and evaluated for DMFC suitability. The semi-IPN SPEEK/PSt-DVB structure provided better dimensional stability, thermal stability, and mechanical integrity than the pristine SPEEK membrane. The methanol diffusion coefficient of the SPEEK/PSt-DVB-30% was reduced approximately by 70% when compared to the value of Nafion-117 at 30°C. The maximum selectivity of the semi-IPN membranes was 9.27 × 104 S s cm−3 for the SPEEK/PSt-DVB-20%, which was nearly 2.1 times higher than that of the Nafion-117 membrane. The improved properties of the SPEEK/PSt-DVB membranes were attributed to the homogeneous semi-IPN structure and to the hydrophobic molecular chains of PSt-DVB.

Preparation of Super-Hydrophobic Polyester Fabric by Growing Polysiloxane Microtube and its Application

In this article, we tried to induce siloxane to form microtubes through the way of self-assembly on the surface of polyester fabric and make the fabric super-hydrophobic. After the polyester fabric coated by silicon microtubes, the modified fabric obtained super-hydrophobicity due to the same property of silicon microtubes. We used the ethyl trichlorosilane to deposit the siloxaneon the surface of the polyester fabrics in the nitrogen condition by vapor deposition method. The structures and properties of modified polyester fabrics were characterized by scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), Fourier transform infrared spectrum (FTIR), Thermogravimetric analysis (TG) and oil/water separation testing. The results showed the silicon microtubes had been formed and the Si takes a high mass proportion in the sample, proving the siloxane had been successfully grown on the surface further. Oil/water separation experiment and water contact angle measurement proved that the modified fabric had high super-hydrophobicity and it’s important for application in various environment.

Synthesis and characterization of aniline-dimer-based electroactive benzoxazine and its polymer

An electroactive aniline-dimer-based benzoxazine (BA–PADPA) was prepared from bisphenol A, p-aminodiphenylamine (PADPA), and paraformaldehyde. The structure of BA–PADPA was successfully confirmed by fourier transform infrared spectroscopy, and 1H-NMR and 13C-NMR spectroscopy. Further, BA–PADPA was polymerized into polybenzoxazine by thermal curing. During the thermally induced polymerization, the imino group of PADPA segment first catalyzed the ring-opening reaction of benzoxazine groups of BA–PADPA at about 161 °C. Subsequently, the autocatalytic benzoxazine polymerization process followed at higher temperatures. Both the curing stages of BA–PADPA were completed at lower temperature ranges than those of the bisphenol A/aniline-based benzoxazine (BA–AN). The activation energies for the amine-catalyzed ring-opening and the autocatalytic benzoxazine polymerization were determined by both the Kissingers and Ozawas methods. Furthermore, the redox behavior of the as-synthesized BA–PADPA polymer (PBA–PADPA) was evaluated by cyclic voltammetry. The results indicated that the PBA–PADPA coating exhibited a satisfactory corrosion resistance ability with a corrosion rate of 0.0108 mm per year for carbon steel Q235, which is significantly lower than that of the BA–AN polymer coating (PBA–AN). Insights were gained into the anticorrosion mechanism, which indicated that the redox catalytic property of the PADPA segments in PBA–PADPA was probably capable of inducing the formation of a metal oxide layer composed of Fe2O3 on the steel surface, which was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. This study provides in-depth investigations and comprehensive understanding of the polymerization behavior of the benzoxazine/aniline-dimer-based system, which are necessary for the design, manufacture, and utilization of this type of high-performance polymeric coating.

Flame retardancy and toughening properties of epoxy composites containing ammonium polyphosphate microcapsules and expanded graphite

Ammonium polyphosphate microcapsules (BM (polybenzoxazine modified) APP) were prepared through the in situ ring-opening polymerization of allyl group containing benzoxazine monomers on the surfaces of ammonium polyphosphate (APP), and they were significantly hydrophobic than the APP. A flame retardant system of epoxy (EP) resin was prepared with BMAPP and expanded graphite (EG). Flame retardancy, the thermal degradation behavior, a mechanical property of EP and EP/BMAPP/EG composites was investigated through limited oxygen index, vertical burning test, cone calorimetry (CONE), and the thermogravimetric analysis (TGA). The flame retardancy tests indicated that the EG could improve the thermal performance, promote the charring, and enhance the char quality of EP/BMAPP. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were employed to analyze the morphology and composition of the char residue formed during CONE testing, and to understand the mechanism of char formation. The results of TG-FTIR confirmed the possible mechanism of flame retardancy of EP/BMAPP/EG in the gas phase during combustion. The EG content effects on Young’s modulus, the tensile strength, and the fracture toughness (K IC) of the EP/BMAPP composites were also investigated. The K IC of the composites containing 1% of EG and 10% of BMAPP increased by approximately 76% and 153%, respectively, compared to the neat matrix and EP/BMAPP-10%. The SEM images of the fractured surface indicated that the enhanced toughness of EP/BMAPP/EG composites mainly attributed to the debonding of the BMAPP and the subsequent plastic void growth of the matrix, as well as the crack deflection effect of the BMAPP/EG.

Growth of Zinc Oxide Nanorods in Alocohol Solution

Zinc oxide (ZnO) nanorods have been grown by hydrolyzing Zn(OAc) 2 •2H 2 O in methanol solution. Nanoparticles in sizes ranging from 2 to 4 nm were first obtained at low concentration. The growth kinetics was monitored by UV-vis absorption spectroscopy. The precursor was then concentrated by 10 folds and refluxed at 60°C for 24 hours to form ZnO nanorods with an aspect ratio of 12. Ligand adsorption growth model was proposed to explain the anisotropic growth.